Collected on this day...

Giant hogweed (Heracleum mantegazzianum) is considered a significant public human health concern. This non-woody plant can be 8-20 feet tall with leaves up to 5 feet wide! In fact, it took 6 separate herbarium sheets to capture the characteristics of this species. This specimen was collected from a garden, where it was intentionally grown for the purposes of educating the public about this plant. Native to central and southwest Asia, this plant can now be found in parts of Europe, Australia, New Zealand, and North America. It is thought to be eradicated in Pennsylvania.

This plant is highly poisonous and designated as a federal noxious weed. The sap of giant hogweed causes “phytophotodermatitis,” meaning serious skin inflammation occurs when contacted skin is exposed to sunlight. Skin rashes can be very severe. The sap is also said to cause blindness.

Giant hogweed, like poison hemlock and Queen Anne’s lace, is in the carrot family (Apiaceae). It might be confused with the related native plant, cow parsnip (Heracleum lanatum), but giant hogweed is noticeably larger in height and flower size.

Collected on June 23, 1993, this specimen was found by Fred Utech near the Loyalhanna Creek in Salem Township, PA.

Don’t let the “weed” in common name affect your opinion of this plant! Butterfly weed (Aclepias tuberosa) is a beautiful plant and the pollinators love the bright orange flowers. Native to eastern North America, it can be found in dry, full sun conditions. It is a great plant to add to your garden!

Like other milkweeds (butterfly weed is in the milkweed genus), butterfly weed flower clusters mature into seed pods which eventual dry up to release airborne seeds in the late summer. The long silk-like hairs (called pappi, or singular: pappus) have been used by native Americans to make textiles.

Despite its looks, butterfly weed is poisonous to ingest. Like other milkweeds, this plant contains defensive chemicals called cardiac glycosides, which are poisonous to humans, livestock, and pets. Milkweeds vary in their toxicity depending on species and age of plant. Symptoms can include: weakness, difficulty breathing, kidney damage, cardiac distress, pupil dilation, loss of muscle control, and respiratory paralysis.

Butterfly weed flowers open early- to mid-summer (above).Seeds burst from pods and blow in the wind in late summer (below).

Collected on June 16, 1925, this specimen was found near Shinglehouse, Potter County, PA by H.W. Graham.

Poison ivy (Toxicodendron radicans) is a species you might be very familiar with! Poison ivy is a native woody vine found in wooded areas, along paths, and edges of woods across the eastern United States.the species can take various forms and habits, growing as a vine along the ground, up a tree, or as a small shrub.

Poison ivy is famous for a chemical it produces, urushiol, which upon contact, can cause a severe skin rash in humans. The rash, which can last up to several weeks, can also lead to an infection due to intense scratching that breaks the skin. Serious health effects can stem from ingesting urushiol or can cause other allergic reactions in eyes and throat when inhaling smoke from burned plants. If you come into contact with poison ivy, the best way to prevent an allergic reaction is washing with water and soap (or other detergent to wash off oils) as soon as possible. Some people are more sensitive to poison ivy than others, or become more sensitive after repeated exposure.

Poison ivy is in the cashew plant family (Anacardiaceae), which includes several other species which produce skin irritants. In addition to poison ivy, poison oak, and poison sumac, the family also includes mango and cashew. Interestingly, the shell of the cashew nut contains chemicals that can cause similar allergic skin reactions as poison ivy.

You might have heard “Leaves of three, let it be,” but what does that mean exactly? And how do you know if it is poison ivy, poison oak, or poison sumac? Many plants might at first glance resemble poison ivy, but they can be easily distinguished. Poison ivy is common in woods, forest edges, roadsides, and weedy areas throughout Pennsylvania, and has aerial, hairy-looking rootlets on stems of vines. Poison sumac (Toxicodendron vernix) is also native to Pennsylvania, but is less common and only found in swamps and other persistently wet habitats. Poison sumac (Toxicodendron vernix) has leaves made up of many more leaflets than poison ivy. Lastly, poison oak (Toxicodendron diversilobum) is sometimes confused with poison ivy, but it is unlikely you encountered this species in Pennsylvania -- it is only native to the western United States.

Left: Poison ivy (Toxicodendron radicans), common in woods, trails, and forest edges in PAMiddle: Poison oak (Toxicodendron diversilobum), you might be out WestRight: Poison sumac (Toxicodendron vernix), you might be in a swamp

Collected on June 9, 1959, this specimen was in the woods along a road to Pocahontas, near Salisbury in Somerset County, PA by Leroy Henry. Henry was the Curator of Botany at the museum.

Mountain laurel (Kalmia latifolia) is the state flower of Pennsylvania! It is a broadleaved evergreen shrub native across the eastern US, especially in forests of mountainous areas. This specimen was collected not too far from the highest point in Pennsylvania and the Maryland border. Often mistaken for Rhododendron, both the Rhododenrons and mountain laurel are found in similar habitats and belong to the heath family (Ericaceae).

Despite its beauty, mountain laurel has a dark side: all parts contain toxins that are poisonous to humans, pets, horses, and cattle. Ingesting this plant can cause vomiting, diarrhea, impaired vision, convulsion, cardiovascular distress and death. Honey made by bees from mountain laurel can also cause medical problems to humans. Benjamin Smith Barton (American botanist in late 1700s) wrote that “in the autumn and winter of the year 1790, many people died in Pennsylvania from the effects of wild honey, collected from Kalmia plants.”

Poison hemlock (Conium maculatum) was used to kill the Greek philosopher Socrates in 399 BC. All parts of the plant are highly toxic, containing an alkaloid poison, coniine, which disrupts the central nervous system and can cause paralysis of respiratory muscles and death.

Although native to Europe, poison hemlock has been introduced to the United States and found in the Pittsburgh region. Despite the name, it is not related to hemlock trees, but instead a member of the carrot family (Apiaceae). Carrot family members are often recognizable by their flowers, which are on stalks that spread from a common point to form umbrella-like clusters (botanically called an “umbel”).

Keep an eye out for this species. It is blooming now in our region along roadsides and ditches. Towering at heights over 9 feet tall, this plant is hard to miss if you look for it. Aside from its height, it can also be distinguished from similar species by the purple blotches on the stems. It is best to avoid contact with this species, it can be fatal if ingested but can also cause skin irritations if touched.

It has been introduced for a while now, but seems to be getting more common in some areas of region.

Collected on June 2, 1994, this specimen was found along Neshannock Creek in Mercer County, PA by Bonnie and Joe Isaac. Bonnie is the collection manager in Botany at the museum. She and her husband, Joe, are both professional botanists and active collectors. Over 20,000 specimens in the Carnegie Museum herbarium have been collected by them.

Garlic mustard (Alliaria petiolata) is a non-native species from Europe that invades roadsides and forest understories across the eastern US, often displacing native species. Garlic mustard has also been shown to produce chemicals that inhibit the growth of fungi in the soil that form a symbiotic relationship with the roots of many native forest species. It has also been shown to be facilitated by overabundant deer. Garlic mustard was introduced from Europe and first reported in Long Island in 1868. However, it was not widely recognized as a widespread invasive species until the early 1980s. Scientists are using herbarium specimens to study the introduction and map the spread of this invasive species through time.